The present invention relates to an exposing apparatus for preparing documents such as color proofs, slides, OHP (overhead projector) sheets, transparencies, copies, and facsimile documents. More particularly, the invention is directed to an exposing apparatus and a method for forming images using such exposing apparatus, in which a heat-developed photosensitive recording medium that produces color images using only heat developing is exposed in a simple manner without causing crosstalk and without use of additional sheets.
The invention may be applied extensively to color proofs, slides, OHP sheets, transparencies, copies, and facsimile documents, etc. While the invention will hereunder be described while taking a color proof as an example for convenience, it goes without saying that the invention provides similar effects in its other applications.
Color proofs can be produced by various methods, each of which has some shortcomings.
An overlay method is a typical color proof producing method. This method reproduces an image by overlaying films of different colors. It is essential that the image be observed through the films, thus impairing the quality of the image.
As a method for producing an image on a single sheet, a sur-print method is available. This method produces an image by sequentially superimposing four color photosensitive films on a single substrate. While "Chromarine" (E.I. DuPont Co.), "Match Print" (3M Co.), and "Color Art" (Fuji Photo Film Co., Ltd.) are known as sur-print methods, all of these methods require four photosensitive films and consequently produce waste.
A color paper method in which a color image is formed on a single photosensitive sheet is also known. This method forms a color image by causing a film original to contact a sheet of color paper, exposing the color paper using filters of different colors, and subjecting the exposed paper to a wet developing process. "Fine Checker" (Fuji Photo Film Co., Ltd.) and "Consensus" (Konishiroku Photo Industry Co., Ltd.) are known versions of this method. This method, wherein the photosensitizing range of the color paper falls within a visible range, involves the requirement that the process be performed in a darkroom or with an exposing device having a light-tight chamber. Moreover, significant maintenance and management are required for the developing solution.
All of these methods have shortcomings, such as requiring a plurality of sheets, producing waste including transfer sheets and toner, and involve difficulties in handling in a bright room, or in calling for a developing system using a developing solution.
To obviate the above shortcomings, a method has been proposed which employs a heat-developed photosensitive recording medium that forms a latent image on a photocuring composition by exposure and forms a color image by causing a component to be diffused within the photosensitive material in accordance with the latent image, the component having to do with coloring or discoloring by heating. The method forms a color image by passing an original of the image into an exposing section, exposing the photosensitive recording medium, forming a latent image by photocuring at the exposing section, thereafter diffusing a nonphotocured portion having to do with coloring or discoloring by heating the photosensitive recording medium, and forming a visible image. This is a completely dry system producing no waste.
Several photosensitive recording media are available for this method. While these media are advantageous in forming monochromatic images, they are more advantageous when used as color recording media.
An exemplary recording medium is disclosed, e.g., in Japanese Patent Unexamined Publication No. 89915/1977. This medium is prepared by arranging two components of a binary thermosensitive coloring media, e.g., an electron accepting compound and an electron donating achromatic dye, either inside and outside a microcapsule containing a photocuring composition or so as to be separated from each other on both sides of the microcapsule. However, this medium allows the photocuring composition within the microcapsule to be sufficiently hardened, but cannot suppress the coloring of the photocured portion adequately. As a result, the nonimage portion does get slightly colored, thereby exhibiting a tendency to impair the contrast.
A more preferred medium free from such coloring of the nonimage portion is disclosed, e.g., in Japanese Patent Unexamined Publication No. 123838/1986. This recording media is a lamination formed of a layer incorporating a photopolymerizing composition consisting of a vinyl monomer having an acid base and a photopolymerization initiator, an isolating layer, and an electron-donating achromatic dye. With this medium, a substantial absence of thermal diffusion of the acid base in a portion hardened by the nonimage portion, i.e., the photopolymerized portion, leads to elimination of the coloring of the nonimage portion, but the coloring density is somewhat low.
As a method for obtaining a negative image by a similar method, a method disclosed, e.g., in Japanese Patent Unexamined Publication No. 119552/1985 is known. This method involves use of a recording medium in which a photopolymerizing composition consisting of a monomer or prepolymer for bleaching a coloring matter and a photopolymerization initiator coexists with the coloring matter to be bleached by the monomer or prepolymer so as to be isolated from each other. This material also has problems similar to those of the above media.
The most preferred medium that has overcome the problems of coloring the nonimage portion and reducing the image density is a medium disclosed in co-assigned Japanese Patent Unexamined Publication No. 87827/1991. In this medium, one of the two components of a binary thermosensitive coloring medium is enclosed in microcapsules, and the other component is arranged outside the microcapsules as a curing compound of a photocuring composition or together with the photocuring composition.
A negative image producing medium based on a similar concept is disclosed in co-assigned Japanese Patent Application No. 16788/1991. This recording medium has a coating of a layer consisting of a photopolymerizing composition containing an electron accepting compound, a copolymerizing vinyl monomer, and a photopolymerizing initiator outside microcapsules, with the microcapsules containing an electron-donating achromatic dye.
To produce a color recording with these photosensitive recording media, a recording medium having a plurality of photosensitive layers whose photosensitizing wavelengths and hues to be obtained by heat development are different from one another may generally be used. The recording media disclosed in Japanese Patent Unexamined Publication No. 87827/1991 and Japanese Patent Application No. 16788/1991 are exemplary preferred multicolor recording media. For example, a multicolor recording medium having a plurality of photosensitive layers, each corresponding to a different color, and such plurality of photosensitive layers consist of at least two photosensitive layers laminated on a substrate from the side of an exposing light source to the side of a carrying body of the recording medium in the order of: a first photosensitive layer which is photosensitized by light whose center wavelength is .lambda.1; an intermediate layer absorbing light whose center wavelength is .lambda.1; a second photosensitive layer which is photosensitized by light whose center wavelength is .lambda.2 and giving a color that is different from a color given by the first photosensitive layer; an intermediate layer absorbing light whose center wavelength is .lambda.i-1; and an i-th photosensitive layer which is photosensitized by light whose center wavelength is .lambda.i and giving a color that is different from the colors given by the first and second photosensitive layers. The multicolor recording medium also satisfies the following relationship among the center wavelengths: EQU .lambda.1&lt;.lambda.2&lt; . . . &lt;.lambda.i
where i is a positive integer not less than 2.
This photosensitive recording medium, being of a monosheet type, absorbs visible light rays when its center wavelength .lambda.j is set to the visible range, j being not less than 1, thus causing itself to be colored. For this reason, it is desirable that the center wavelength be out of the ultraviolet range. In the case of a photosensitive recording medium having coloring layers for cyan, magenta, and yellow, it is desirable to set three different center wavelengths outside the ultraviolet range. More specifically, it is desired that the three center wavelengths be limited within about 120 nm between about 450 nm and 330 nm, which is the widest possible range. The lower limit 330 nm is the shortest wavelength which the supporting glass plate of the exposing apparatus and a lith original can transmit, whereas the upper limit 450 nm or so is a wavelength that permits the recording medium to be colored.
On the other hand, it is necessary to use, as exposing light sources for exposing this photosensitive recording medium, light rays of the respective three regions into which this narrow range of about 120 nm is divided. The requirement is that a light source of a single color be used to photosensitize only a single coloring layer, and to meet this requirement, a bandpass filter is desirably used. An interference filter, with which a sharp bandpass filter whose half-width is narrow can be designed, is advantageous. However, when trying to divide this narrow range of about 120 nm into three regions using an ordinary planar interference filter, a troublesome phenomenon called "crosstalk" may occur.
For example, when exposing the photosensitive recording medium in the region of a wavelength .lambda.2, crosstalk with components .lambda.1 and/or .lambda.3 of the injected light passing through the filter photosensitize photosensitive layers other than the .lambda.2 photosensitive layer may occur. An image obtained from the development of the photosensitive recording medium which is affected by such crosstalk produces a color different from the color expected from the original.
Further, since the interference filter is expensive, it is desirable to use a smaller interference filter, which, in turn, requires that the interference filter be disposed adjacent to the light source. When the interference filter is located adjacent to the light source, the interference filter gets heated by the heat produced by the light source. It has further been found, surprisingly, that bandpass characteristic of the interference filter changes with increasing temperature, drifting the transmitted light region to about 10 nm. As a result, the transmitted light extends beyond each region that is about 40 nm or less in width.
Accordingly, while these photosensitive recording media exhibit excellent properties in experimental terms, no system capable of forming images which are practically large enough has been developed yet.